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Trouble code libraryFuel and air

P0172 Engine is running rich (bank 1)

Generic SAE definitionSystem too rich (Bank 1)

Drive gentlyYou can drive it, but take it easy and get it looked at soon – waiting usually makes the repair bigger.

Check this first

Check the air filter – a blocked filter is the cheapest cause of a rich mixture.

Rich running washes oil off the bores and can ruin a catalytic converter, so don't leave it.

What usually fixes it

In the order a good shop checks them. Typical total: $62–$725 at $130 an hour.

  1. Air filter

    $62–$135

    A blocked filter starves the engine of air.

  2. Leaking fuel injector

    $268–$725

    An injector that drips adds fuel nobody asked for.

  3. Fuel pressure regulator

    $206–$494

    Too much pressure pushes extra fuel through every injector.

  4. Oxygen sensor

    $128–$350

    A lazy sensor makes the computer keep adding fuel.

Code titles are the generic SAE definitions. Prices are typical US parts and labor for a common car or light truck – a guide for judging a quote, not a quote. Always confirm a repair against the vehicle in front of you.

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See what your vehicle says about P0172

A stored code is a headline, not the story. The vehicle also holds the conditions from the moment the code set, how close each part is to the limit it fails at, what the fuel trims are doing, and whether the fault is still happening. Drive DTC reads all of it with a USB adapter and a Windows PC – read-only by design.

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More in Fuel and air

All 73 codes in this group
P0159O2 sensor circuit slow response (Bank 2 Sensor 2) P0161O2 sensor heater circuit (Bank 2 Sensor 2) P0171System too lean (Bank 1) P0174System too lean (Bank 2) P0175System too rich (Bank 2) P0191Fuel rail pressure sensor A circuit range/performance